The "resting" peripheral blood lymphocyte of the rabbit may be stimulated to undergo "blast" transformation by a variety of mitogenic agents including certain lectins (PHA, Con A), anti-immunoglobulin and antiallotypic antibodies, and anti-lymphocytic sera. The mechanism of induction of this activation is unknown. The studies proposed by this application are designed to delineate early membrane events during blast transformation and metabolic events occurring during stimulation, blocking and restimulation in vitro. The distribution of surface immunoglobulins during transformation (activation), de-activation (blocking) and re-activation will be determined by a mixed antiglobulin immunoferritin technique. The type of surface reaction required for stimulation will be studied by the use of agents of different size and valency. The expression of allelic determinates will be determined by direct labelling and mixed sequential antiallotypic stimulation. The results should lead to a better understanding of the effect of differentiation upon genetic expression and of the induction events required for lymphocyte activation.